Gravity separation of coal ore



J y 1966 P. M. YAVORSKY ETAL 3,261,559

GRAVITY SEPARATION OF COAL ORE 5 Sheets-Sheet 1 Filed Aug. 7, 1961 RAW COAL FEED MIDDLINGS INVENTORS. PAUL M. YAVORSKY RESIDUE BY EVERETT GORIN 5 J ,VJ L

THEIR ATTORNEY FLUlDlZlNG--+- WATER y 1966 P. M. YAVORSKY ETAL 3,261,559

GRAVITY SEPARATION OF COAL ORE Filed Aug 7, 1961 5 Sheets-Sheet 2 U z t Z 2 3 u. w

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INV EN TOR$ PAUL M. YAVORSKY EVERETT GORIN THEIR ATTORNEY y 1966 P. M. YAVORSKY ETAL 3,261,559

GRAVITY SEPARATION OF COAL ORE 3 SheetsSheet 5 Filed Aug 7, 1961 wDQmmm 3 256mm r. g 28.- 23+ $5.592 Wm 28 EB 28 25 6 INVENTORS PAUL M. YAVORSKY BY EVERETT GORIN FQL THEIR ATTORNEY United States Patent 3,261,559 GRAVITY SEPARATION OF COAL ORE Paul M. Yavorsky, Monongahela, and Everett Gorin,

Pittsburgh, Pa., assignors to Consolidation Coal Conrpany, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 7, 1961, Ser. No. 129,610 4 Claims. (Cl. 24124) This invention rel-ates to the separation of a mixture of particulate material having particles of different specific gravity into fractions having like specific gravities. More particularly this invention relates to the separation of coal from higher specific gravity inorganic impurities by fluidizing a mixture of the coal and impurities in a liquid medium within a vessel until the particles of coal and impurities assume predetermined positions within the vessel, and withdrawing separately coal and impurities from the vessel.

Coal as it is mined contains inorganic impurities such as slate, rock, clay and other inorganic matter.

It is the principal object of this invention to separate the coal particles from these impurities.

One type of impurity that is found in raw coal and which presents problems in its separation from the coal is pyritic sulfur or pyrites. The pyrites (FeS is often found as layers or bands Within the coal strata. Grains of pyrites and other impurities are also found dispersed throughout the coal strata. It has been found that a substantial percentage of the pyrites and other inorganic impurities can be exposed and detached from the coal particles by grinding or crushing the raw coal particles to a relatively small size. The small sized particles then contain particles of pure pyrites, mixed grain particles, and relatively pure coal particles. The mixed grain particles contain grains of coal, pyrites and other inorganic impurities. The mixed grain particles are of varying density between a density of 1.30 which is substantially pure coal and a density of 5.0 which is the density of the pure pyrites. The density of the mixed grain particles depends on the relative ratio of the grains of impurities and grains of pure coal in each particle. In other words, the mixed grain particles contain a Whole spectrum of particles of varying density between that of clean coal and substantially pure pyrites.

Until the present invention no satisfactory method has been found for separating either pure pyrites particles or particles rich in pyrites and other inorganic impurities from the clean coal without an undue loss of clean coal. This is particularly true in the range of small sized particles that will pass through a 100 mesh Tyler Standard screen. The present invention provides a novel method and novel apparatus for efiiciently separating pyrites and pyrites-rich particles from relatively pure coal particles. It will be appreciated that the present invention is also useful in removing other inorganic impurities from coal by segregating the particles according to their specific gravity. Throughout this specification the term raw coa will be utilized to designate coal as it is mined and containing pyrites and other inorganic impurities.

Pyrites (PeS has a specific gravity of between 4.5 and 5.5. Clean coal, on the other hand, has a specific gravity of between about 1.25 and 1.35. By utilizing the dif ference in specific gravity between the coal particles and the pure pyrites particles or mixed grain particles rich in pyrites, the present invention efiiciently segregates the coal Patented July 19, 1966 particles and the pyrites particles to enable the clean coal to be recovered separately from the pyrites particles. The present invention is not only capable of segregating the relatively high specific gravity pyrites particles and the relatively low specific gravity coal particles, but may also be used in segregating mixed grain particles which may have a smaller differential in specific gravity than that of coal and pyrites. For example, it is believed the present invention can effectively segregate mixed grain particles having a difierence in specific gravity of .2.

In addition to the above, one of the unique advantages of the present invention is a method of preparing a clean coal-water slurry that may be used alone or admixed with other coal particles as a slurry suitable for transportation through a long distance pipeline. When employed for this purpose the dewatering of the slurry is not required. For certain applications, sufiicient water can be removed from the slurry to provide a clean coal-Water slurry of the desired concentration by weight of clean coal particles.

The present invention utilizes the principle of liquid fluidization to separate particles having diiferent specific gravities. The mixture of particles having difierent specific gravities is introduced into a fiuidizing vessel. A lquid, for example water, is passed upwardly through the mixture at a predetermined linear velocity. The liquid suspends the particles within the fluidizing vessel and the particles segregate according to their specific gravity with the particles of lower specific gravity assuming a position within the vessel adjacent the upper portion of the vessel and the particles of higher specific gravity assuming a position adjacent the lower portion of the vessel. The segregated particles having substantially the same specific gravity may then be removed from the upper, intermediate and lower portions of the vessel. The above description presumes that the particles are of substantially the same size.

If the particles are of different sizes as well as being of different specific gravities, the position that each particle assumes within the fluidizing vessel will be a function of both its particle size and its specific gravity. Thus, if the particles have a spectrum of sizes and different specific gravities, the smallest of the lower specific gravity particles will assume a position near the top of the vessel while the largest of the high specific gravity particles will assume a position near the bottom of the vessel. In various zones throughout the vessel a mixture of large particles having a low specific gravity will assume a position similar to small particles having a higher specific gravity. When a large particle having a low specific gravity and a small particle having a high specific gravity assume substantially equivalent positions Within the fluidizing vessel, as a lquid is passed upwardly through the vessel at a predetermined linear velocity these particles are, under such conditions, hydrodynamically equivalent.

The present invention contemplates introducing raw coal into a fiuidizing vessel and passing a liquid upwardly through the vessel at a predetermined linear velocity. The raw coal particles are permitted to reach equilibrium positions within the fluidizing vessel. Once the equilibrium positions are reached for each particle, the particles may be withdrawn as a slurry from various zones in the fluidizing vessel. If desired, the slurries may be dewatered to provide a relatively dry product, used as is, or concentrated if use as a coal-Water slurry for transportation through a pipeline is considered. The particles withdrawn from the various zones of the vessel Will be either substantially clean coal, or combinations of relatively large sized clean coal particles, intermediate sized mixed grain particles and relatively small sized particles of substantially pure pyrites, or larger sized particles rich in pyrites and other inorganic impurities.

The above gravity and size distribution is obtained because the relatively low gravity large sized clean coal particles, the intermediate gravity mixed grain particles, and the relatively small sized heavy gravity pyrites particles attain hydrodynamic equivalency within the vessel. When the large sized clean coal particles, the intermediate sized mixed grain particles and the smaller relatively pure pyrites particles are removed together, the product may be termed middlings, which is a mixture of various gravity material ranging from relatively large sized particles of clean coal through intermediate sized mixed grain particles containing both coal, pyrites and other impurities in mixed grains, and small relatively pure pyrites particles. The middlings product of the present invention is such, however, that it may be readily screened to separate the large sized clean coal particles from the intermediate sized mixed grain particles and the smaller sized relatively pure pyrites particles. This is accomplished by the present invention because the different sized and different gravity particles in the middlings product are withdrawn as a single stream. The large clean coal particles may be easily separated from the smaller pyrites particles and the intermediate sized mixed grain particles by means of conventional screening apparatus or other suitable separating means. middlings product may be introduced into another fluidization vessel in which the fiuidizing liquid is of a higher density than water.

Throughout the specification the'separation of relatively pure coal particles from pyrites particles will be discussed. It should be understood, however, that included Within the clean coal particles will be mixed grain particles containing a relatively small number of grains of pyrites or other inorganic impurities. In a like manner the pyrites particles will include mixed grain particles that are rich in pyrites and other inorganic impurities and yet contain grains of pure coal in small amounts.

The present invention contemplates a fiuidizing vessel constructed in the form of a vertical column into which the raw coal is introduced and through which a current of liquid is passed upwardly. It has been found that it is essential to maintain the flow of fiuidizing liquid in a substantially streamline or non-turbulent state. It is highly undesirable to permit turbulent flow of the fiuidizing liquid because the turbulence causes intermixing of the particles and reduces the effective segregation within the vessel according to specific gravity. In order to insure upward streamline flow of the liquid through the fluidizing vessel, a series of vertical baflles are provided to maintain the streamline flow. At various vertical positions in the column outlet pipes are provided so that particles may be withdrawn from the vessel as a slurry. The fluidizing vessel may be operated either on a continuous basis or on a cyclic batch-wise basis. The particles may be withdrawn from the vessel through a plurality of outlet pipes as above described, or withdrawn through a single outlet pipe adjacent the bottom of the vessel. When withdrawn through a single outlet the particles within the slurry may be classified according to specific gravity by a gravity measuring means and dewatered separately to recover different gravity products.

The present invention also contemplates a trough type fiuidizing vessel which separates the particulate material as it is conveyed laterally as a slurry through the vessel. A fiuidizing liquid is introduced along the bottom of the trough type fiuidizing vessel and flows upwardly therethrough. The mixture of different gravity material while being conveyed laterally is segregated according to specific For example, the

gravity and is withdrawn as a slurry from diiferent zones of the vessel. The trough type fiuidizing vessel is particularly suited for continuous operation.

The present invention also contemplates a two stage separation of particulate material. It has been found that the fiuidizing vessel of the present invention operates more efiiciently when the spectrum of particle sizes of raw coal introduced into the separator is not excessively wide. For example, if a wide range of particles is introduced Which contains very large particles as well as very small particles with intermediate sizes therebetween, the upward linear velocity of the fiuidizing liquid must be relatively high since the largest of the low gravity particles should be suspended within the fiuidizing vessel for proper gravity separation. It is desirable that the largest of the low gravity particles be held in suspension so that they are not mixed with the heavy gravity particles that are found at the bottom of the fiuidizing vessel. It the linear velocity of the fiuidizing liquid is such that the largest particle of low gravity material is suspended, it has been found that an excessive amount of low gravity small particles is carried over with the fiuidizing liquid. This condition is also undesirable for accurate gravity segregation within the vessel.

In order to minimize the above undesirable conditions, the present invention further contemplates an initial screening of the raw coal to divide the large spectrum of particle sizes into two smaller spectrums consisting of a large particle spectrum which remains on the screen, and a small particle spectrum which passes through the screen. The large particle spectrum may then be introduced into a relatively high velocity fiuidizing vessel since this spectrum is substantially free of small particles having a low specific gravity which would, under conditions of high linear velocity of the fiuidizing liquid, be carried upwardly through the vessel with the fiuidizing liquid. The small particle spectrum is introduced into a fiuidizing vessel wherein the upward current of fiuidizing liquid has a low er linear velocity so that the smaller particles are efiiciently separated. The linear velocity of the fiuidizing liquid need only be sufficient to suspend the largest of the low specific gravity particles. The largest of the low specific gravity particles, in the small particle spectrum, will be much smaller than the largest particle of the low specific gravity particles in the large particle spectrum.

With the foregoing considerations in mind, it' is a primary object of the present invention to provide a method of efiiciently separating particulate material into a plurality of specific gravity fractions.

Another object of this invention is to provide a method of separating particles having .a spectrum of particle sizes and different specific gravities into a fraction in which particles having a low specific gravity may be withdrawn substantially free of particles having a high specific gravity.

Another object of this invention is to provide a method of separating difierent specific gravity particles by means of fiuidizing the different gravity particles in a liquid 50 that the lower gravity particles assume a position in the fiuidizing liquid above the particles having a high specific gravity.

Another object of this invention is to provide a method of separating particles having a spectrum of particle sizes and dilferent specific gravities into fractions of which one fraction has large particles of lower specific gravity materials and small particles of high specific gravity materials, and separating the larger sized low specific gravity material'from the smaller sized high specific gravity material by means of size classification alone.

Another object of this invention is to provide a method of separating particles having a spectrum of particle sizes and ditferent specific gravities by first separating the particles generally into two particle size fractions and thereafter treating each size'fraction separately to separate the low gravity material from the high gravity material.

These and other objects of this invention will become apparent from the following description, the accompanying drawings, and the appended claims.

In the drawings, FIGURE 1 is a vertical sectional elevation taken along the line 11 of FIGURE 2 illustrating a fiuidizing vessel built in accordance with the principles of the present invention.

FIGURE 2 is a top plan view of the vessel of FIG- URE 1.

FIGURE 3 is a perspective semi-schematic view of a second type of fiuidizing vessel.

FIGURE 4 is a schematic flow diagram showing one manner of utilizing the fiuidizing vessels of this invention to efficiently remove the impurities from raw coal.

Referring to FIGURES l and 2 there is shown a fluidizing vessel generally designated by the numeral 10. The vessel has a cylindrical upper portion 12, an intermediate frusto conical portion 14, and a cup shaped lower portion 16. A fiuidizing liquid inlet 18 is connected to the bottom of the cup shaped lower portion 16 and provides a means for introducing fiuidizing liquid into the vessel 10. An overflow trough is provided along the upper edge of the cylindrical upper portion 12. The overflow trough 20 is provided with an outlet conduit 22. The fiuidizing water introduced into vessel 10 through inlet 18 fiows upwardly through the vessel 10 at a predetermined linear velocity and is collected on the overflow trough- 20 and withdrawn therefrom through conduit 22. The water withdrawn through conduit 22 may be recirculated to the fiuidizing water inlet 18 in a conventional manner if desired to provide a substantially closed liquid system.

The cylindrical upper portion 12 has a plurality of withdrawal conduits 24 and 26 through which slurries of particulate material and liquid may be withdrawn. The cylindrical upper portion 12 also has a raw coal inlet conduit 28 through which the coal in the form of a slurry is introduced into the fiuidizing vessel 10. It will be appreciated that the raw coal may be introduced as a particulate feed by conventional means instead of as a slurry if desired.

The cup shaped lower portion 16 has a first outlet 30 through which a mixture of large sized low gravity material and small sized high gravity material may be withdrawn. The lower cup shaped portion 16 has a second outlet conduit 32 through which high gravity particulate material may be withdrawn as a slurry. The various conduits 22, 24, 26, 28, 30 and 32 are appropriately valved by means of valves 34 to control the flow of material therethrough.

Within the vessel 10 there are a plurality of vertical bafiles 36 arranged in checkerboard fashion as best seen in FIGURE 2 to form rectangular chambers 38 in the vessel 10. The bafiles 36 are provided with a plurality of apertures 40 so that there is communication between the various chambers 38. It will be appreciated that the chambers 38 within vessel 10 provide a means for maintaining streamline non-turbulent flow upwardly through the fiuidizing vessel 10.

In utilizing the fiuidizing vessel illustrated in FIGURES 1 and 2 it was found that raw coal having a spectrum of particle sizes all of which would pass through an 8 mesh Tyler screen (termed 8 x 0) could be separated into different gravity fractions. When 8 X 0 raw coal was utilized it was found that a minimum linear velocity for the fluidizing liquid was .013 ft./sec. This was the velocity required to maintain the largest low gravity particles in a suspended state. It was found where the velocity exceeded .025 ft./sec. substantial amounts of fine coal particles were carried over with the fiuidizing liquid and did not remain suspended Within the fiuidizing vessel 10.

Where 8 x O raw coal is employed, an inventory of the 8 X 0 raw coal is introduced into the fiuidizing vessel 10 through raw coal feed inlet pipe 28. A fiuidizing liquid, preferably water, is introduced into the fiuidizing vessel 10 through the liquid inlet '18 and passes upwardly 6 through the vessel 10 and overflows into the trough 20 and is withdrawn from the vessel 10 through outlet 2-2. The fiuidizing liquid is circulated through the vessel 10 at a linear velocity of between .013 ft./sec. and .025 ft./ sec. The fiuidizing liquid is continually circulated through the vessel 10 at the above linear velocity until the particles within the vessel 10 segregate according to their specific gravity and size. For example, a layer of heavy gravity substantially pure pyrites particles forms near the bottom of the cup shaped portion 16. A middlings layer forms above the layer of pyrites particles within the cup shaped portion 16. The middlings layer contains large sized particles of substantially clean coal, a substantial amount of mixed grain particles of intermediate gravity, and relatively small sized particles of substantially pure pyrites. The cylindrical upper portion 12 contains substantially clean coal particles which are suspended according to size since they are all of substantially the same specific gravity. The substantially clean coal particles may be removed from the cylindrical upper portion of vessel 10' through outlets 24 and 26. The smaller sized clean coal particles may be removed through outlet 24 and the larger sized clean coal particles may be removed through outlet 26. The middlings fraction may be removed through outlet 30 in the cup shaped lower portion 16 and the substantially pure pyrites may be removed through outlet 32. If desired, the entire inventory of 8 x 0 particles may be removed from the vessel 10 through outlet 32. The first fraction to be withdrawn through outlet 32 would be the substantially pure pyrites particles. The second fraction withdrawn would be the middlings fraction containing a mixture of large sized coal particles, intermediate gravity mixed grain particles, and small sized pyrites particles. The third fraction withdrawn is the clean coal particles. In this manner all the particles may be removed through a single outlet and subsequently separated according to their specific gravity. The fluidizing water passing upwardly through vessel 10 may carry over a small amount of extremely fine coal particles. These fine coal particles may be separated from the fiuidizing liquid in any conventional manner before the liquid is again recirculated to the fiuidizing vessel.

It will be appreciated that the relative size of the raw coal particles introduced into the fiuidizing vessel will dictate the linear velocity of the fiuidizing liquid for most desirable gravity segregation. Further, a plurality of outlet pipes may be provided in the upper cylindrical portion of the fiuidizing vessel 10' so that clean coal at predetermined sizes may be withdrawn from the fiuidizing vessel.

It Will be appreciated that the process described may be operated either batchwise, continuously, or as a semicyclic operation. The principal prerequisite that should be observed is that there is a sufiicient hold-up time of the particulate material within the fiuidizing vessel 10 to permit the particles to segregate into various zones according to their specific gravity.

Referring to FIGURE 3 there is shown a fiuidizing vessel generally designated by the numeral 42 which is particularly adapted for continuous separation of different gravity material. The fiuidizing vessel 42 has a generally rectangular enclosed portion 44 with a sloping bottom portion 46 formed of fiuidizing screens 48. Beneath the fiuidizing screens 48 there is a fiuidizing trough '50. Fluidizing water is introduced into fiuidizing trough 50 through a common conduit 52 and a plurality of vertical inlet pipes 54. The fiuidizing Water introduced into the fiuidizing vessel 42 through common conduit 52 and vertical inlet conduit 54 passes upwardly through the fiuidizing trough 50 through the screens 48 and overflows over the top of the vessel 42 into a trough 56 which extends around the periphery of the vessel 42. The fiuidizing water is withdrawn 'from the trough 56 through conduit 58 which may be connected by any conventional means with fiuidizing liquid inlet conduit 52. Suitable pumping means and control means may be provided to provide the predetermined linear velocity of the liquid as it passes upwardly through the fluidizing vessel 42. At the upper end of the vessel 42 there is a raw coal inlet conduit 60. At the other end of the vessel 42 there is a plurality of the residue outlet. Above the outlet conduit 62 there is a middlings outlet conduit 64 through which a mixture of large sized clean coal particles and small sized pyrites particles are withdrawn from the vessel 42. Above the middlings conduit 64 there are a pair of clean coal withdrawal conduits 66 and 68 through which clean coal of different sizes is Withdrawn. Appropriate valving 70 is provided in all conduits to control the feed to the fluidizing vessel 42 and the withdrawal of product therefrom.

When raw coal is admitted through conduit 60 it flows laterally toward the lower portion of the vessel 42. Fluidizing water, introduced through common conduit 52 and vertical inlet pipes 54, passes upwardly through the screens 48 and suspends the particles of raW coal. The upward flow of the fluidizing water classifies the raw coal particles as previous-1y described in connection with FIGURES l and 2. The particles rich in pyrites and other inorganic impurities are withdrawn through residue outlet conduit 62, the middlings are withdrawn through outlet conduit 64 and the clean coal is withdrawn through outlet conduits 66 and 68. The fluidizing water overflows the vessel 42 into trough 56 and is withdrawn through conduit 58.

FIGURE 4 is a schematic diagram of a coal cleaning process embodying the process for separating particulate material according to specific gravity. As shown in FIG- URE 4 a raw coal slurry having a spectrum of particle sizes, all of which would pass through an 8 mesh Tyler screen (8 x is introduced onto a splitter screen 72. Screen 72 is preferably a 48 mesh Tyler screen. All particles passing through screen 72 are particles having a size less than 48 mesh (48 or 48 x 0). All particles remaining on screen 72 are of a size greater than 48 mesh (+48 or 8 x 48). The 8 x 48 mesh particles from screen 72 are directed to a fluidizing vessel 74 which is preferably of the type shown in FIGURES 1 and 2. Fluidizing liquid is introduced into the fluidizing vessel 74 at a relatively high linear velocity. The high velocity fluidizing vessel 74 classifies the particles into clean coal, middlings, and residue. The clean coal from vessel 74 is transported directly to drag tank 76. The middlings from vessel 74 are transported to a screen 78. It has been found that the middlings fraction withdrawn from the high velocity fluidizing vessel 74 has a substantial portion of clean coal with a size greater than 20 mesh. The middlings fraction is substantially free of pyrites particles having a size greater than 20 mesh.

There is, however, in the middlings fraction from the high velocity fluidizing vessel 74 a substantial amount of mixed grain particles which have a higher than average coal content than is present in the residue. Accordingly, the 20 mesh fraction of the middlings product is transported to a comminuting means 80 where the size of the 20 mesh material is reduced to substantially all 48 mesh. The 48 mesh product from the comminuting means 80 is transported to and introduced into a low velocity fluidizing vessel 82. i

It has been found when the entire fraction including the +20 mesh material or the 20 mesh fraction is subjected to comminution in a comminuting means to reduce the size of the particles to substantially all 48 mesh, the mixed grain particles are fractured in a manner that particles of relatively clean coal are liberated from the mixed grain particles, that is the comminuted 48 mesh product contains a substantial number of particles of relatively clean coal. The ---20 mesh product fed to the comminuting means in comparison contains few, if any, particles of substantially clean coal. The purpose of the comminuting of the middlings fraction is, therefore, to liberate more clean coal particles from the outlet conduits the lowermost of which, 62, may be termed mixed grain particles. If desired, instead of screening the middlings fraction to a +20 mesh and 20 mesh fraction, the entire middlings product may be introduced into the comminuting means 80. Alternatively, the middlings fraction may be screened on a 20 mesh screen and the +20 mesh clean coal from screen 78 may be combined with the clean coal withdrawn from the high velocity fluidizing vessel 74. The combined product is then transported directly to a drag tank 76. The comminution of the +20 mesh fraction of the middlings product assists in optimizing the production of fines required for a coal-water slurry that is transported through a long distance pipeline.

The 48 x 0 material from screen 72 and the 48 mesh product from comminuting means 80 are directed to the low velocity fluidizing vessel 82. A fluidizing liquid, preferably water, is introduced into the bottom of fluidizing vessel 82 and passed upwardly therethrough at a substantially reduced linear velocity when compared with the linear velocity of the liquid passing upwardly through fluidizing vessel 74. Within fluidizing vessel 82 the raw coal is classified as previously described so that clean coal may be removed from the upper portion of fluidizing vessel 82 and transported directly to the drag tank 76. The middlings fraction removed from the fluidizing ves sel 82 may be screened on a '65 mesh Tyler screen 84. It has been found that substantially all of the particles in the middlings fraction having a size greater than 65 mesh Tyler screen are substantially clean coal particles. Particles having a size less than 65 mesh are mixed grain particles which contain a higher than average coal content when compared with particles present in the residue. The +65 mesh particles which pass over the screen 84 are transported directly to the drag tank 76. The particles passing through screen 84 are transported to a second comminuting means 86 where they are all reduced in size to below mesh. The product from the comminuter 86 is introduced into an elutriator 88 which has water flowing upwardly therethrough at a substantially high velocity. The water entrains the 100 mesh clean coal particles after it passes upwardly through the elutriator 88. The water and 100 mesh clean coal particles from the elutriator 88 are then transported to drag tank 76 or any other suitable separating means wherein the Water is separated from the clean coal particles. The remaining pyrites rich particles in the 100 mesh material are withdrawn from the elutriator 88 and discarded.

Alternatively, the entire middlings product from the low velocity fluidizing vessel 82 may be introduced directly into comminuting means 86 where substantially all of the particles are reduced to a size below 100 mesh. The purpose of the comminuting means 86 is, as previously stated, to liberate more clean coal particles from the mixed grain particles. This is accomplished by fracturing the mixed grain particles. The separating means 76 is described, for exemplary purposes only, as a drag tank. It is appreciated that other means may be employed to concentrate the slurry, especially the slurry containing coal particles having a size less than 48 mesh. For example, thickeners or hydrocyclones could be employed to concentrate the slurry product from the fluidizing vessels. Further, it will be appreciated that other separating means may be employed to separate the +100 mesh clean coal particles from the 100 mesh mixed grain and relatively pure pyrites particles. The comminuting means 80 and 86 are of conventional construction.

The process described and illustrated in FIGURE 4 provides for the efficient separation of clean coal from a mixture of clean coal and heavy gravity impurities such as pyrites. It will be appreciated that various size fractions of the clean coal may be employed separately rather than combining all fractions in a single collecting means. It will be further appreciated that the schematic diagram illustrated in FIGURE 4 is for illustrative purposes only and the invention may be practiced other than as specifically illustrated and described.

The following examples, which are meant to be illustrative and not limiting, illustrate the effective separation of clean coal from a mixture of clean coal and heavy gravity inorganic material.

EXAMPLE I.-SINGLE FLUIDIZING OPERATION [Coal feed: 8 mesh x The feed coal in the foregoing example was raw coal that contained 13.8 percent impurities in the form of inorganic matter. Sulfur accounted for 31.4 percent of the total impurity. Sulfur was present in two forms-- inorganic sulfur, i.e. pyrites, and organic bound sulfur. The latter form of sulfur was not separable by the above process because the sulfur was molecularly bound in the coal molecule. The organically bound sulfur comprised about 36 percent of the total sulfur present. It is appar- I cut, therefore, even if perfect gravity separation were obtained, the clean coal product would contain 1.56 percent sulfur.

The raw coal in the above example was comminuted to 8 mesh x 0 and was introduced into a fiuidizing vessel. The raw coal was fluidized within the vessel with water as the fluidizing medium. Three products were withdrawn from the fluidizing vessel, namely clean coal, middlings, and residue. The middlings product Was screened on a 14 mesh Tyler screen and separated into a +14 mesh fraction and a +14 mesh fraction. The +14 mesh fraction was combined with the clean coal product and the +14 mesh fraction was combined with the residue product resulting in two final products-clean coal and residue.

By the above method it was possible to recover 91 percent of the pure coal introduced into the process and reduce the overall sulfur content from 4.31 percent to 2.76 percent and the pyritic sulfur from 2.75 percent to 1.20 percent. The overall percent of inorganic impurities was reduced in the above process from 13.8 percent to about 8.2 percent.

EXAMPLE II.DOUBLE FLUIDIZIN G OPERATION [Raw coal feed: 8 x 0 mesh] Content of Material Material Total Pure Inorganic Percent Wt.,1b. Coal, Matter, Sulfur lb. lb.

Feed Coal 100 86. 8 13. 2 4. 20 Clean Coal From 8 x 48 mesh Fluidizer and 48 x 0 Fluidizer 89. 1 81. 1 8. 0 2. l0 Combined Residue 10. 9 5. 7 5. 2 21.4

minuted middlings product was combined with the 48 mesh fraction of the raw coal feed and introduced into a low velocity fluidizer. Three products were withdrawn from the low velocity fluidizer-clean coal, middlings and residue. The clean coal product of the low velocity fluidizer, the middlings product of the low velocity fluidizer and the clean coal product of the high velocity fluidizer were combined as a single clean coal product. The remaining residue products of the low velocity fluidizer and the high velocity fluidizer were combined as a single residue product. As is evident from the above data, it is now possible using the two fluidizing methods taught herein, to recover 93.4 percent of the pure coal in the raw coal feed and to reduce the overall sulfur content from 4.2 percent to 2.1 percent and the pyritic sulfur from 2.64 percent to .54 percent.

It will be appreciated that the effectiveness of the above process to separate clean coal from heavy gravity inorganic material varies with the ease with which the pyrites rich particles are liberated by comminution. The effectiveness of the process can be quickly determined by lab oratory float-sink type gravity determination of the coal employed. For the particular coal feed employed in Examples I and II the float-sink gravity measurements indicates 2.5 percent sulfur at percent clean coal yield and 2.7 percent sulfur at 93 percent clean coal yield. The process of Example II shows a lower sulfur content than the ultimate predicted by float-sink which is impossible by hydraulic classification alone. The ability to obtain clean coal with a lower sulfur content resides in recomminuting the middlings fraction. If the middlings fraction of the material used in a float-sink analysis were comminuted in a similar manner, the float-sink results would show an equal or lower sulfur content. Thus, by the relatively simple float-sink and comminuting operation one can determine the effectiveness of the previously described process on various types of coal.

According to the provisions of the patent statutes, we have explained the principle, preferred construction, and mode of operation of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

1. A method of separating coal particles from a mixture of coal particles and pyrite particles which comprises comminuting said mixture to a predetermined spectrum of sizes containing coal particles having a spectrum of sizes and pyrites particles having a spectrum of sizes, introducing said mixture into a separating vessel, passing substantially clear water upwardly through said vessel at a linear velocity sufiicient to suspend the largest particle of said coal and maintain substantially all of said coal particles suspended in said water and within said vessel, controlling the velocity of said Water passing upwardly through said vessel to form within said vessel a first zone of particles adjacent the upper portion of said vessel and a second zone of particles adjacent the lower portion of said vessel, said first zone containing coal particles of small size and being substantially free of said pyrites particles, said second zone containing a mixture of coal particles of large size and said pyrites particles, withdrawing a stream of said water from said first zone, said stream including said coal particles, separating said coal particles from said water, withdrawing a stream of said water from said second zone, said stream including a mixture of coal particles and pyrites particles, said coal particles in said mixture being larger than said pyrites particles, and passing said stream from said second zone over a screen and separating said water and said pyrites particles from said 'larger sized coa-l particles.

2. A method of separating a mixture of raw coa'l having a spectrum of sizes including large size particles and small size particles, said mixture of raw coal having particles of different specific gravity including particles of inorganic material having a relatively high specific gravity of between about 2.5 and about 5.5 and coal particles having a relatively low specific gravity of between about 1.25 and about 1.35, said method comprising introducing said mixture into a separating vessel, passing a substantially clear liquid upwardly through said vessel at a linear 'velocity sufficient to suspend said coal particles and certain of said smaller particles of inorganic material in said liquid within said vessel, the specific gravity of said liquid 'being less than the specific gravity of the lightest of said particles, controlling the linear velocity of said liquid fiowing upwardly in said vessel so that said particles within said vessel form an upper zone adjacent the upper portion of said vessel, said upper zone comprising coal particles of small size, an intermediate zone having a mixture of particles comprising coal particles of large size and particles of inorganic material of small size, a lower zone comprising large size particles of inorganic material, withdrawing a first stream of said liquid from said upper zone containing said coal particles and separating said coal particles from said liquid, withdrawing a second stream of said liquid from said intermediate zone containing said mixture of large size coal particles and said small size particles of inorganic material, separating said mixture according to size into said small particles of inorganic material and said large sized coal particles, and withdrawing a third stream from said lower zone containing said high gravity particles of inorganic material.

'3. A method of separating a mixture of raw coal having a spectrum of sizes with a top size of about 8 mesh, said mixture having particles of different specific gravity including pyrites particles of high specific gravity between about 4.5 and about .5 and coal particles of low specific gravity of between about 1.25 and about 1.35, said method comprising introducing said mixture into a separating vessel, passing a substantially clear liquid upwardly through said vessel at a linear velocity suificient to suspend said coal particles and certain of said smaller pyrites particles in said liquid Within said vessel, the specific gravity of said liquid being less than the specific gravity of the lightest of said particles, controlling the linear velocity of said liquid flowing upwardly in said vessel -0 that said particles within said vessel form an upper zone adjacent the upper portion of said vessel, said upper zone including coal particles of small size, an intermediate zone including a mixture of coal particles of large size and pyrites particles of small size, a lower zone including pyrites particles of large size, withdrawing a first stream of said liquid from said upper zone containing said coal particles and separating said coal particles fromsaid liquid, withdrawing a second stream of said liquid from said intermediate zone containing said mixture of large size coal particles and said small size pyrites particles, separating said mixture according to size into said small pyrites particles and said large coal particles and withdrawing a third stream of said liquid from'said lower zone containing pyrites particles.

4. The method of separating a mixture of raw coal having a spectrum of particle sizes with a top size of about 8 mesh, said mixture having particles of different specificgravity including pyrites particles of high specific gravity and coal particles of low specific gravity, said method comprising separating said mixture of raw coal by size into a first quantity having a spectrum of particle sizes greater than about 48 mesh and a second quantity having a spectrum of particle sizes less than 48 mesh, introducing said first quantity into a first separating vessel, passing substantially 'clearwater upwardly through said first vessel at a relatively. high linearvelocity, sulfihigh gravity pyrites particles of small size, withdrawing a first stream from said upper zone including coal particles and water, withdrawing a second stream from said intermediate zone containing a mixture of large coal particles, small size pyrites particles and water, passing said second stream over a 20 mesh screen to recover coal particles hav- ..ing a size greater than 20 mesh, sai-d remaining portion of said second stream containing a mixture of coal and pyrites particles, comminuting said remaining portion of said second stream to a size less than 48 mesh, introducing said comminuted remaining portion of said second stream together with said second quantity of raw coal mixture having a size less than 48 mesh into a second separating vessel, passing substantially clear water upwardly through said second vessel at a relatively low linear velocity sufficient to suspend said coal particles having a low specific gravity and certain of said smaller pyrites particles having a high specific gravity in said water within said second vessel, said particles within said second vessel forming an upper zone adjacent an upper portion of said second vessel, said upper zone including coal particles having low specific gravity, an intermediate zone including a mixture of low gravity coal particles of larger size and high gravity pyrites particles of smaller size, withdrawing 'a third stream from said second vessel upper zone including coal particles having low specific gravity and water, withdrawing a fourth stream from said second vessel intermediate zone containing a mixture of large size low gravity coal particles and small size high gravity pyrites particles, passing said fourth stream over a 65 mesh screen to recover coal particles having a size greater than 65 mesh from said fourth stream, the remaining portion of said fourth stream containing a mixture of coal and pyrites particles, comminuting said remaining portion of said fourth stream to a size less than mesh, and elutriating said comminuted remaining portion of said fourth stream to recover coal having a size less than 100 mesh therefrom.

References Cited by the Examiner UNITED STATES PATENTS 118,379 8/187 1 Merrill 209 594,953 8/11897 Hurt 209158 636,675- -11/ 1899 Latimer 209158 934,441 9/1909 Hitchcock 200158 X 934,611 9/1909 Hitchcock 209160 \1,057,15 1 3/1913 Howard 24124 1,452,815 4/1923 Reed 209454 1,715,693 6/ 1929 Bird 209454 1,959,2'12' 5/1934 Miller 209158 X 2,269,912 :1/ 1942 Ladoo 20924 2,417,660 3/1947 Remick 20912 2,708,517 5/ 1955 Evans 209454 X 2,854,136 9/ 1958 Gillie et a1 209158 2,967,617 1/1961 Evans 209158 FOREIGN PATENTS 7311,2-87 6/1955 Great Britain.

FRANK W. LU'ITER, Primary Examiner.

HARRY B. THORNTON, ROBERT A. OLEAARY,

' Examiners.

H. F. PEPPER, Assistant Examiner. 

1. A METHOD OF SEPARATING COAL PARTICLES FROM A MIXTURE OF COAL PARTICLES AND PYRITE PARTICLES WHICH COMPRISES COMMINUTING SAID MIXTURE TO A PREDETERMINED SPECTRUM OF SIZES CONTAINING COAL PARICLES HAVING A SPECTRUM OF SIZES AND PYRITES PARTICLES HAVING A SPECTRUM OF SIZES, INTRODUCING SAID MIXTURES INTO A SEPARATING VESSEL, PASSING SUBSTANTIALLY CLEAR WATER UPWARDLY THROUGH SAID VESSEL AT A LINEAR VELOCITY SUFFICIENT TO SUSPEND THE LARGEST PARTICLE OF SAID COAL AND MAINTAIN SUBSTANTIALLY ALL OF SAID COAL PARTICLES SUSPENDED IN SAID WATER AND WITHIN SAID VESSEL, CONTROLLING THE VELOCITY OF SAID WATER PASSING UPWARDLY THROUGH SAID VESSEL TO FORM WITHIN SAID VESSEL A FIRST ZONE OF PARTICLES ADJACENT THE UPPER PORTION OF SAID VESSEL AND A SECOND ZONE OF PARTICLES ADJACENT THE LOWER PORTION OF SAID VESSEL, SAID FIRST ZONE CONTAINING COAL PARTICLES OF SMALL SIZE AND BEING SUBSTANTIALLY FREE OF SAID PYRITES PARTICLES, SAID SECOND ZONE CONTAINING A MIXTURE OF COAL PARTICLES OF LARGE SIZE AND SAID PYRITES PARTICLES, WITHDRAWING A STREAM OF SAID WATER FROM SAID FIRST ZONE, SAID STREAM INCLUDING SAID COAL PARTICLES, SEPARATING SAID COAL PARTICLES FROM SAID WATER, WITHDRAWING A STREAM OF SAID WATER FROM SAID SECOND ZONE, SAID STREAM INCLUDING A MIXTURE OF COAL PARTICLES AND PYRITES PARTICLES, SAID COAL PARTICLES IN SAID MIXTURE BEING LARGER THAN SAID PYRITES PARTICLES, AND PASSING SAID STREAM FROM SAID SECOND ZONE OVER A SCREEN AND SEPARATING SAID WATER AND SAID PYRITES PARTICLES FROM SAID LARGER SIZED COAL PARTICLES.
 4. THE METHOD OF SEPARATING A MIXTURE OF RAW COAL HAVING A SPECTRUM OF PARTICLE SIZES WITH A TOP SIZE OF ABOUT 8 MESH, SAID MIXTURE HAVING PARTICLES OF DIFFERENT SPECIFIC GRAVITY INCLUDING PYRITES PARTICLES OF HIGH SPECIFIC GRAVITY AND COAL PARTICLES OF LOW SPECIFIC GRAVITY, SAID METHOD COMPRISING SEPARATING SAID MIXTURE OF RAW COAL BY SIZE INTO A FIRST QUANTITY HAVING A SPECTRUM OF PARTICLE SIZES GREATER THAN ABOUT 48 MESH AND A SECOND QUANTITY HAVING A SPECTRUM OF PARTICLE SIZES LESS THAN 48 MESH, INTRODUCING SAID FIRST QUANTITY INTO A FIRST SEPARATING VESSEL, PASSING SUBSTANTIALLY CLEAR WATER UPWARDLY THROUGH SAID FIRST VESSL AT A RELATIVELY HIGH LINEAR VELOCITY, SUFFICIENT TO SUSPEND SAID COAL PARTICLES HAVING A LOW SPECIFIC GRAVITY AND CERTAIN OF SAID SMALLER PYRITES PARTICLES HAVING A HIGH SPECIFIC GRAVITY IN SAID WATER WITHIN SAID FIRST VESSEL, SAID PARTICLES WITHIN SAID FIRST VESSEL FORMING AN UPPER ZONE ADJACENT AN UPPER PORTION OF SAID FIRST VESSEL, SAID UPPER ZONE INCLUDING COAL PARTICLES OF SMALL SIZE HAVING LOW SPECIFIC GRAVITY, AN INTERMEDIATE ZONE INCLUDING A MIXTURE OF LOW GRAVITY COAL PARTICLES OF LARGE SIZE AND HIGH GRAVITY PYRITES PARTICLES OF SMALL SIZE, WITHDRAWING A FIRST STREAM FROM SAID UPPER ZONE INCLUDING COAL PARTICLES AND WATER, WITHDRAWING A SECOND STREAM FROM SAID INTERMEDIATE ZONE CONTAINING A MIXTURE OF LARGE COAL PARTICLES, SMALL SIZE PARTICLES AND WATER, PASSING SAID SECOND STREAM OVER A 20 MESH SCREEN TO RECOVER COAL PARTICLES HAVING A SIZE GREATER THAN 20 MESH, SAID REMAINING PORTION OF SAID SECOND STREAM CONTAINING A MIXTURE OF COAL AND PYRITES PARTICLES, COMMINUTING SAID REMAINING PORTION OF SAID SECOND STREAM TO A SIZE LESS THAN 48 MESH, INTRODUCING SAID COMMINUTED REMAINING PORTION OF SAID SECOND STREAM TOGETHER WITH SAID SECOND QUANTITY OF RAW COAL MIXTURE HAVING A SIZE LESS THAN 48 MESH INTO A SECOND SEPARATING VESSEL, PASSING SUBSTANTIALLY CLEAR WATER UPWARDLY THROUGH SAID SECOND VESSEL AT A RELATIVELY LOW LINEAR VELOCITY SUFFICIENT TO SUSPEND SAID COAL PARTICLES HAVING A LOW SPECIFIC GRAVITY AND CERTAIN OF SAID SMALL PYRITES PARTICLES HAVING A HIGH SPECIFIC GRAVITY IN SAID WATER WITHIN SAID SECOND VESSEL, SAID PARTICLES WITHIN SAID SECOND VESSEL FORMING AN UPPER ZONE ADJACENT AN UPPER PORTION OF SAID SECOND VESSEL, SAID UPPER ZONE INCLUDING COAL PARTICLES HAVING LOW SPECIFIC GRAVITY, INTERMEDIATE ZONE INCLUDING A MIXTURE OF LOW GRAVITY COAL PARTICLES OF LARGER SIZE AND HIGH GRAVITY PYRITES OF SMALLER SIZE, WITHDRAWING A THIRD STREAM FROM SAID SECOND VESSEL UPPER ZONE INCLUDING COAL PARTICLES HAVING LOW SPECIFIC GRAVITY AND WATER, WITHDRAWING A FOURTH STREAM FROM SAID SECOND VESSEL INTERMEDIATE ZONE CONTAINING A MIXTURE OF LARGE SIZE LOW GRAVITY COAL PARTICLES AND SMALL SIZE HIGH GRAVITY PYRITES PARTICLES, PASSING SAID FOURTH STREAM OVER A 65 MESH SCREEN TO RECOVER COAL PARTICLES HAVING A SIZE GREATER THAN 65 MESH FROM SAID FOURTH STREAM, THE REMAINING PORTION OF SAID FOURTH STREAM CONTAINING A MIXTURE OF COAL AND PYRITES PARTICLES, COMMINUTING SAID REMAINING PORTION OF SAID FOURTH STREAM TO A SIZE LESS THAN 100 MESH, AND ELUTRIATING SAID COMMINUTED REMAINING PORTION OF SAID FOURTH STREAM TO RECOVER COAL HAVING A SIZE LESS THAN 100 MESH THEREFROM. 